This invention relates generally to hardening resin compositions of solventless type. More specifically, the invention relates to oil-modified alkyd resin compositions which can be applied as coatings to form coating films of excellent hardness, resistance to bending, resistance to impacts, property of being applicable as thick layers (thereinafter referred to as thickly applicable property), and resistance to water. The term "paint" is herein used to designate collectively coating materials such as paints, varnishes, enamels, coating compounds, and the like.
Still more specifically, the invention relates to improvements in the water resistance and hardness of the paint ingredients in the ingredient system of my prior invention disclosed in my previous Japanese Patent Application No. 44317/1976
In general, oil-modified alkyd resins are prepared from polybasic acids, polyhydric alcohols, and saturated or unsaturated fatty acids or oils. These oil-modified alkyd resins are being used for various paints such as paints for drying at room temperature, the characteristic of these resins to harden as a result of participation of the double bond of the unsaturated fatty acid in the composition in a bridging or cross-linking reaction because of the oxygen in air being utilized.
Under the assumption that the fatty acid or oil in the resin in an oil-modified alkyd resin has reacted with glycerine to form a triglyceride, the weight percentage of the triglyceride in the resin is called the oil length. This oil length is closely related to the physical properties such as solubility, hardness, luster or gloss, color retentivitiy, weather resistance, hardening time, and preservability of the paint. For example, while an increase in the oil length results in an increase in the flexibility of the paint film and its solubility in organic solvents, it tends to decrease the hardness of the paint film. On the other hand, a decrease in the oil length is useful in improving the luster and color retentivity of the paint film but tends to decrease the spreadability of the paint. Of course, the oil length is not the only factor influencing the above mentioned physical properties of the paint, these properties being influenced also by the properties of the other ingredients of the oil-modified alkyd resin.
Heretofore, oil-modified alkyd resins of oil lengths of the order of 30 to 80 percent have been generally dissolved in solvents such as turpentine oil and toluene and used in room temperature drying paints and baking paints. However, oil-modified alkyd resin paints diluted by such solvents are accompanied by problems such as long drying times and pollution of the working environment by the evaporation of the solvents at the time of drying.
Oil-modified alkyd resin paints in which solvents are not used, that is, paints of the solventless type (which may be called pollutionless type) in which all paint ingredients react, are now being studied. However, those that have been developed to date have been accompanied by problems such as poor adhesion to metals, inadequate mechanical properties such as impact resistance and bending resistance, and inadequate coating property and have not been reduced to practical use, as far as I am aware.
In order to solve these problems, I have previously proposed oil-modified alkyd resins comprising the following ingredients as disclosed in the patent applications cited hereinbefore.
1. An oil-modified alkyd resin composition comprising:
(A) 50 to 80% by weight of an oil-modified alkyd resin which is modified with a fatty acid containing at least 65% by weight of linoleic acid and/or linolenic acid and has an oil length of 40 to 70%; and PA1 (B) 50 to 20% by weight of an acrylate and/or methacrylate which is a monoester of an alcohol having from 2 to 20 carbon atoms and acrylic acid or methacrylic acid.
This paint composition has the advantages of excellent adhesion to metals and short hardening time, thereby possessing great practicability. However, it requires approximately one day to produce a water resistant film therefrom. For this reason, there has been a great demand for improvement of these compositions for obtaining water resistant films in a short time particularly in the fields of structures exposed to the atmosphere such as bridges, production plants, and ships.